The present invention relates to a signal processing apparatus for performing product-sum operations and, more particularly, to a digital filter.
Japanese Laid-Open Patent Publication SHO 58-162120 has disclosed a signal processing apparatus which functions as a transversal filter. The signal processing apparatus is composed of a plurality of signal processing elements (SPEs) connected in cascade and comprises a first path for transferring an input data signal and a second path for transferring a processing result of the input data signal. Each of the SPEs comprises a first input disposed on the first path and a second input disposed on the second path. Each of the SPEs further comprises: three latches for holding three respective data signals supplied sequentially through the first input; a first selector for sequentially selecting the three data signals held in the three latches; a second selector for sequentially selecting three coefficients in response to the first selector; a multiplier for sequentially calculating respective products of the data signals selected by the first selector and the coefficients selected by the second selector; an accumulator for accumulating the three products obtained in the multiplier; and an adder for calculating a sum of the result of accumulation performed by the accumulator and a data signal supplied through the second input, i.e., a partial sum. The data signal held in the last one of the three latches of each SPE is supplied to the first input of the SPE in the subsequent stage, thereby constituting a shift register on the first path. On the other hand, the data signal representing the partial sum obtained in the adder of each SPE is supplied to the second input of the SPE in the subsequent stage. To implement a 9-tap transversal filter, three SPEs are connected in cascade.
In a television set, it is generally required to perform a sequence of processes, such as a vertical filtering process and a horizontal filtering process to be sequentially performed, with respect to an image data signal. In addition, it is strongly desired to process image data signals in different broadcasting systems by means of a single signal processing apparatus.
However, a signal processing apparatus with the foregoing internal structure in which the plurality of SPEs are connected in cascade has the disadvantage of insufficient flexibility. Once the signal processing apparatus has been formed, the number of taps for a filtering process is fixed depending on the number of the SPEs that have been connected. For example, a signal processing apparatus composed of three SPEs is dedicated to a 9-tap filter and hence cannot function as three sequential 3-tap filters.